1. Field of the Invention
The invention relates to a system for displaying images and, more particularly, to a system for displaying images including organic electroluminescent diode.
2. Description of the Related Art
Organic electroluminescent diodes are self-emitting and highly luminous, have a wide viewing angle, faster response, and a simple fabrication process, making them an industry display of choice. Recently, with the development and wide application of electronic products such as mobile phones, personal digital assistants, and notebook computers, there has been an increased demand for flat display devices which consume less power and occupy less space.
Conventional organic electroluminescent diodes, however, generally rely on intrinsic semiconductor materials and have undoped hole injection layers, exhibit higher driving voltage and power consumption in comparison with the same type of liquid crystal display (LCD). In order to reduce the driving voltage and power consumption of organic electroluminescent diodes, an OLED having a p-i-n structure is described in Huang et al., Low Voltage Organic Electroluminescent Devices Using pin Structures, Applied Physics Letters, Vol. 80, No. 1, pp 139-141 (2002). In particular, the OLED has a p-doped hole injection layers.
Stephen R. Forrest disclosed a p-i-n OLED using F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane) as p-dopant and m-MTDATA (4,4′,4″-tris(3-methylphenylphenylamino)-triphenylamine) as host of a p-doped layer to achieve a driving voltage of not more than about 2 volts at a current density of 100 cd/m2. Because the F4-TCNQ has low thermal stability and is apt to be decomposed during evaporation, the reliability and performance of the OLED is reduced. Further, due to the low deposition temperature of F4-TCNQ, the dopant amount of the F4-TCNQ is difficult to control.
Therefore, it is necessary to develop a p-i-n OLED employing a novel material with improved thermal stability and optoelectronic characteristics to serve as p-dopant in order to accommodate wide use.